DNA methylation mediates BmDeaf1-regulated tissue- and stage-specific expression of BmCHSA-2b in the silkworm, Bombyx mori

Abstract

BackgroundAccurate regulation of tissue- and stage-specific expression of genes is prerequisite for normal development in organisms. DNA methylation plays an important role in modulating gene expression in mammals and plants. However, there is no direct evidence showing how DNA methylation regulates gene transcription in insects.ResultsDuring the development of Bombyx mori wing, the expression level of DNA methyltransferase 1 (BmDnmt1) gradually declined and became stationary at pupal stage, resulting in a lower methylation rate of the intragenic promoter of the mid-pupal wing-specific gene BmCHSA-2b, an epidermal chitin synthase controlling mid-pupal wing development in B. mori. The higher methylation rate of the promoter in the pupal epidermis was decreased and BmCHSA-2b transcription was significantly increased by the treatment with the DNA methylation inhibitor, 5-azacytidine-2′-deoxycytidine, suggesting that DNA methylation regulates the tissue-specific expression of BmCHSA-2b. Pupa-specific transcription factor BmDEAF1 bound to the unmethylated intragenic promoter and activated the BmCHSA-2b transcription in the mid-pupal wing. BmDnmt1 and BmDeaf1 influenced the BmCHSA-2b transcription by binding competitively to the CpG island in the promoter.ConclusionsAll the data together demonstrate that the cooperation between the down-regulation of BmDnmt1 and increased stage-specific expression of BmDeaf1 enhances BmCHSA-2b tissue- and stage-specific transcription to ensure mid-wing development in B. mori. This study highlights an elaborate regulation mechanism how tissue- and stage-specific gene expression is regulated through promoter methylation in insect development.Electronic supplementary materialThe online version of this article (10.1186/s13072-018-0202-4) contains supplementary material, which is available to authorized users.

The Roles of DNA Methyltransferases 1 (DNMT1) in Regulating Sexual Dimorphism in the Cotton Mealybug, Phenacoccus solenopsis

“…This observation may indicate that PsDnmt1 is important during embryonic and tissue development in the cotton mealybug [54][55][56]. In the silkworm, Bombyx mori, the BmDnmt1 gene is essential to ensure wing development by regulating tissue-and stage-specific transcription of BmCHSA-2b [57].…”

DNA methylation suppresses chitin degradation and promotes the wing development by inhibiting Bmara-mediated chitinase expression in the silkworm, Bombyx mori

“…Whether and how intragenic DNA methylation enhances insect gene expression is unknown. Recently, DNA methylation on gene promoter regions in Drosophila and B. mori was reported [21,24]. Dmkrh1 of juvenile hormone regulatory pathway promotes the hypermethylation of DmSpok promoter region, reducing the transcriptional activity of DmSpok gene [21].…”

“…The chitin content in the wing is a balance of chitin synthesis and chitin degradation, which are catalyzed by chitin synthases and chitinases [40], respectively. Our previous study demonstrated that DNA methylation regulates the expression of chitin synthetase gene BmCHSA-2b in the B. mori pupal wing discs [24]. However, the question whether DNA methylation is engaged in B. mori wing development by affecting chitin content has not been addressed.…”

“…In order to investigate whether and how DNA methylation impacts the wing development, we used DNA methylation inhibitor 5-aza-dC to treat B. mori since Bmdnmt1 RNAi did not work in pupae and 5-aza-dC has been shown to effectively inhibit DNA methylation in B. mori [24]. Dot blot and immunofluorescent staining with 5mC antibody showed that injection of 5-aza-dC in newly molted pupae (P0) induced the de-methylation of 5mC in the genome (Fig.…”

“…Interestingly, the B. mori possesses only one DNA methyltransferase BmDnmt1, but exhibits 5mC DNA methylation [22], suggesting that BmDnmt1 may have dual functions of both de novo methylation and maintenance methylation [20,23]. Our previous work showed that BmDnmt1 RNAi enhanced the transcription of a chitin synthase gene BmCHSA-2b, and 5-aza-dC treatment obtained a similar effect as RNAi [24], indicating that BmDnmt1 play a regulatory role in gene transcription. However, whether BmDnmt1 has dual functions of both de novo methylation and maintenance methylation need to be investigated.…”